export default "\nuniform vec2 u_Low;\nuniform vec2 u_Size;\n\nvec2 grid(in vec2 coord) {\n    vec2 tex = (coord - u_Low) / u_Size;\n    float s = tex.s;\n    float t = tex.t;\n\n    if (t < 0.0 || 1.0 < t) discard;  // lat out of bounds, so nothing to draw\n\n    return vec2(fract(s), t);  // UNDONE: fract used here only because lon is circular.\n}\n";